The present invention relates generally to chemical mechanical polishing of substrates, and more particularly to a carrier head for chemical mechanical polishing.
Integrated circuits are typically formed on substrates, particularly silicon wafers, by the sequential deposition of conductive, semiconductive or insulative layers. After each layer is deposited, it is etched to create circuitry features. As a series of layers are sequentially deposited and etched, the outer or uppermost surface of the substrate, i.e., the exposed surface of the substrate, becomes increasingly nonplanar. This nonplanar surface presents problems in the photolithographic steps of the integrated circuit fabrication process. Therefore, there is a need to periodically planarize the substrate surface.
Chemical mechanical polishing (CMP) is one accepted method of planarization. This planarization method typically requires that the substrate be mounted on a carrier or polishing head. The exposed surface of the substrate is placed against a rotating polishing pad. The polishing pad may be either a xe2x80x9cstandardxe2x80x9d or a fixed-abrasive pad. A standard polishing pad has durable roughened surface, whereas a fixed-abrasive pad has abrasive particles held in a containment media. The carrier head provides a controllable load, i.e., pressure, on the substrate to push it against the polishing pad. Some carrier heads include a flexible membrane that provides a mounting surface for the substrate, and a retaining ring to hold the substrate beneath the mounting surface. Pressurization or evacuation of a chamber behind the flexible membrane controls the load on the substrate.
A polishing slurry, including at least one chemically-reactive agent, and abrasive particles, if a standard pad is used, is supplied to the surface of the polishing pad. The chemical and mechanical interaction between the polishing pad, slurry and substrate results in polishing.
The effectiveness of a CMP process may be measured by its polishing rate, and by the resulting finish (absence of small-scale roughness) and flatness (absence of large-scale topography) of the substrate surface. The polishing rate, finish and flatness are determined by the pad and slurry combination, the relative speed between the substrate and pad, and the force pressing the substrate against the pad.
A reoccurring problem in CMP is the so-called xe2x80x9cedge effectxe2x80x9d, i.e., the tendency of the substrate edge to be polished at a different rate than the substrate center. The edge effect typically results in overpolishing (the removal of too much material from the substrate) at the substrate perimeter, e.g. the outermost five to ten millimeters of a 200 mm wafer.
Another problem, particularly in the polishing of a substrate using a carrier head with a flexible membrane, is binding of the flexible membrane to the retaining ring. Specifically, the edge of the flexible membrane may xe2x80x9cstickxe2x80x9d to the retaining ring, rather than moving inward (if the chamber is evacuated) or outward (if the chamber is pressurized). This creates an uneven pressure distribution on the substrate which can results in non-uniform polishing or difficultly in chucking the substrate to the carrier head.
In general, in one aspect, the invention is directed to a carrier head for a chemical mechanical polishing apparatus. The carrier head includes a base, a flexible membrane extending beneath the base to provide a mounting surface for a substrate, and a retaining ring surrounding the mounting surface. An edge portion of the flexible membrane extends around an outer surface of a support structure, and the outer surface of the support structure is tapered so as to reduce binding between the flexible membrane and the retaining ring.
Implementations of the invention may include one or more of the following features. The support structure may include a support ring and a clamp, and the edge portion of the flexible membrane may be secured between the clamp and the support ring. The radius of the support structure may be greater at its bottom than at its top. The outer surface of the support structure may include a sloped section, e.g., with an off-vertical angle between about 5xc2x0 and 45xc2x0, and a substantially vertical section.
In another aspect, the invention is directed to a carrier head for a chemical mechanical polishing apparatus. The carrier head has a base, a support structure movably connected to the base, a flexible membrane extending beneath the base to provide a mounting surface for a substrate, and a retaining ring surrounding the mounting surface. An edge portion of the flexible membrane extends around an outer surface of the support structure, and the outer surface of the support structure is tapered to limit contact between the edge portion of the flexible membrane and an inner surface of the retaining ring to reduce binding therebetween.
In another aspect, the invention is directed to a carrier head for a chemical mechanical polishing apparatus. The carrier head includes a base, a flexible membrane extending beneath the base to provide a mounting surface for a substrate, and a retaining ring surrounding the mounting surface. An edge portion of the flexible membrane extends around an outer surface of a support structure, and a gap is formed between the flexible membrane and an inner surface of the retaining ring that is sufficiently wide to reduce binding therebetween.
The width of the gap may be between about 0.5 and 2.0 mm, e.g., about 1.25 mm.
In another aspect, the invention is directed to a carrier head for a chemical mechanical polishing apparatus. The carrier head includes a base, a flexible membrane extending beneath the base to provide a mounting surface for a substrate, and a retaining ring surrounding the mounting surface. An edge portion of the flexible membrane extends around an outer surface of a support structure. The flexible membrane also includes a sidewall portion which is more rigid than the lower surface of the flexible membrane to reduce binding between the retaining ring and the flexible membrane.
Implementations of the invention may include one or more of the following features. The sidewall portion of the flexible membrane may be reinforced, e.g., with cloth, metal or plastic. The flexible membrane may be formed substantially of rubber. Reinforcing fibers or a rigid ring may be molded into the sidewall portion.
Advantages of the invention may include the following. Binding of the flexible membrane to the retaining ring is reduced, thereby improving the finish and flatness of the substrate.
Other advantages and features of the invention will be apparent from the following description, including the drawings and claims.